Reflections on distribution and origin of the halacarid genus Isobactrus (Acari: Halacaridae)

Abstract

Isobactrus is a worldwide-spread genus. Most species live in the upper and middle area of a more or less regularly emerged zone. The species diversity is distinctly higher in the northern than in the southern hemisphere. At present, the genus consists of 29 species. An analysis of the geographical distribution of 36 external morphological characters revealed a uniformity in the combination of states of northern Pacific species, but a heterogeneity in the characters of northern Atlantic species. Several character states demonstrate a distinct north/south or north/tropics/ south distribution. A parsimony analysis revealed basal northern Atlantic clades, a northern Pacific clade that also includes Northern Atlantic species and an Indo-Pacific clade with a tropical area cluster. The present data suggest that the genus Isobactrus evolved in the Palaearctic Ocean and might represent a basal lineage within the family Halacaridae.

Freshwater halacarid mites (Acari: Halacaridae) from Madagascar. New records and the description of a new species

“…In general a fusion of plates seems to be correlated with a life in an environment with mechanical stress (Bartsch 2010). In adults of the above mentioned genus Lobohalacarus all ventral plates are fused, but not the dorsal plates.…”

“…The long-legged C. curiosus Bartsch, 1982, from about 800 m depth (Indian Ocean), bears three and two setae on genua I and II, respectively (Bartsch 1982b). As demonstrated by species of the algae-inhabiting genus Isobactrus (Bartsch 2010), a reduction of the number of setae on the legs is not restricted to species living in and on a sediment. According to the though sparse data set, several of the Isobactrus species living in habitats exposed to long-term or severe desiccation have a lower number of setae on the legs than those living in almost permanently wet habitats.…”

The Halacarid Genus Lohmannella (Halacaridae, Acari): List of Species, Notes on Characters, Distribution, Ecology and a Tabular Key

“…Lohmannella bihamata and L. hureaui (in case the latter one is a separate species), have plumulate fossary setae. Similar plumulate setae, though often less conspicuous, have been mentioned in Makarovana (M. hirsuta (Makarova, 1978) and M. spinosa (Bartsch, 1978, in Bartsch 1978b)); Rhombognathus (e. g., R. peltatus Viets, 1939, in Viets 1939b; and two Isobactrus species (I. hutchinsoni Newell 1947 and I. uniscutatus (Viets, 1939) (in Viets 1939b)) (Newell 1947, Makarova, 1978Bartsch 1978bBartsch , 2003cBartsch , 2010b. Rhombognathus peltatus lives in habitats exposed to swell and hence, the plumosity may help it adhere to the Fig.…”